[kepler-dev] Question about OrderedRecordToken

[Edward A. Lee]

I agree that having a non-commutative add could be a problem...
I'm not sure how serious.  Multiplication is not commutative if
the arguments are matrices, and this doesn't seem to create serious
problems.

I'm really not sure what the right answer is...

I guess since you are the designer, you get to decide!

:-)

Edward


ben leinfelder wrote:
> Edward -
> After some gumshoeing, I've found that, for me, the add operation does 
> naturally order the labels in the result rather than preserving the 
> given order of the ordered record tokens involved.
> Then after some tinkering, I now have it locally so that:
> 
> 'a.add(b)' returns a result in the order of 'a'
> and
> 'b.add(a)' return a result in the order of 'b'
> 
> But that seems wrong because then the addition is not commutative. 
> Perhaps we do need to enforce that the tokens have the same ordering 
> (but I agree that also seems wrong).
> -ben
> 
> 
> On Dec 5, 2009, at 8:24 AM, Edward A. Lee wrote:
> 
>>
>> One possibility would be to not perform the addition if
>> the ordering is not the same.  This would be consistent
>> with the fact that
>>
>>  [x = 1, y = 2] != [y = 2, x = 1]
>>
>> and that their types are different.
>>
>> I'm not sure about this though...
>>
>> Edward
>>
>>
>> ben leinfelder wrote:
>>> Edward,
>>> I'm not sure what determines the order of the result when you add 
>>> ordered record tokens - what do you suppose the order should be? With 
>>> the example you have, I don't see a pattern. It's not even defaulting 
>>> to the RecordToken ordering (alpha).
>>> Does it make sense to have the result use the same ordering as the 
>>> initial operand? Or should the operation fail when the tokens are not 
>>> in the same order (seems severe)?
>>> I'd expect
>>> a.getType()
>>> to return
>>> object([x=int, y=int])
>>> It seems to be deferring to the superclass for getType...something I 
>>> should look into/fix.
>>> Thanks for pointing these out.
>>> -ben
>>> On Dec 4, 2009, at 6:51 AM, Edward A. Lee wrote:
>>>>
>>>> Ben,
>>>>
>>>> I have a question about ordered record tokens.
>>>> In the expression evaluator, I can do:
>>>>
>>>> >> a = [x = 1, y = 2]
>>>> [x = 1, y = 2]
>>>>
>>>> >> c = [y = 2, x = 3]
>>>> [y = 2, x = 3]
>>>>
>>>> >> a + c
>>>> [y = 4, x = 4]
>>>>
>>>> >> c + a
>>>> [y = 4, x = 4]
>>>>
>>>>
>>>> What determines the order in the result?
>>>>
>>>> Also, if I do:
>>>>
>>>> >> a.getType()
>>>> object({x = int, y = int})
>>>>
>>>> This description of the type seems exactly the same as
>>>> the description I get from an (unordered) record token.
>>>> Is this a problem? (I don't really know...)
>>>>
>>>> Thanks!
>>>> Edward
>>>> <eal.vcf>
>> <eal.vcf>
> 
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